I am very rusty now, having been retired for some years, but I was on the 76 from day one, as a senior engineer and I find this accident very strange. If the rod end was engage to past the witness hole, I cannot see why it should pull out just because the lock nut was not tight. From memory there is very little stress on these rods, hydraulics on or off, they only operate the pilot valves.
If the rod had been fitted with just a few threads engaged, then I would think it unlikely that the correct rigging figures could have been obtained. The only way I can see that the servo could have been correctly rigged like that, is for the whole system to have been miss rigged all the way back to the stick, an unlikely scenario.
The rod ends cannot rotate, so are they saying that if the nut is not tight, then chattering is enough to pull the rod apart.